The present invention relates in general to a lead path configuration for an electric device and, more particularly, to an improved lead path configuration for a generator rotor used in a power generation plant.
Many power generation plants produce electricity by converting energy (e.g. fossil fuel, nuclear fusion, hydraulic head and geothermal heat) into mechanical energy (e.g. rotation of a turbine shaft), and then converting the mechanical energy into electrical energy (e.g. by the principles of electromagnetic induction).
Some of these power generation plants, such as a fossil-fuel power generation plant, comprise a turbine, a generator and an exciter. The turbine, generator and exciter are typically coupled to each other in axial alignment, with the generator located between the turbine and the exciter.
The turbine converts fossil fuel energy into mechanical energy in the form of turbine shaft rotation through a steam or combustion cycle. The generator then converts the rotational energy into electrical energy. The generator includes an axially extending rotor journaled in an annular stator that surrounds and sleeves the rotor. The rotor has a shaft in which conductive coil windings are axially arranged. The stator has punchings that collectively from an annular core in which conductive coil windings are positioned parallel with respect to the axial rotor coils. As the turbine shaft rotates the generator rotor, the exciter provides an electrical current to the rotor coil windings. The rotating electrically charged rotor creates a magnetic flux that induces an electrical current in the stationary stator coil windings. This induced electrical current is then drawn from the stator and constitutes the electricity that the power generation plant provides to electricity consumers.
One aspect of the above-described power generation scheme involves the electrical interconnection of the exciter and generator. An electrically conductive lead path is used to transport current in a closed loop configuration from the exciter, through the generator rotor coil windings, and then back to the exciter. It has been observed that, as a result of prolonged generator use, the lead path can physically sever or otherwise fail to properly carry current. Among other things, lead path failure can cause electric arcing or re-routing of the electric current through nearby conductive materials. Arcing and re-routing can, among other things, melt portions of the generator shaft and otherwise damage the generator.
It has also been observed that some portions of the lead path tend to fail more often than other portions of the lead path. In particular, it has been observed that lead path failure tends to occur along a portion of the lead path around area A shown in FIG. 2.
There is thus a need for a lead path that inhibits, if not prevents, lead path failure. There is also a need for a portion of a lead path that is particularly suited to inhibit, if not prevent, lead path failure path around area A shown in FIG. 2. There is further need for a lead path that improves upon the prior art.
The present invention provides a lead path that inhibits, if not prevents, lead path failure, especially around area A shown in FIG. 2. The present invention also provides a method of assembling or fitting the lead path of the present invention into a generator. The present invention further provides a method of repairing or retrofitting a lead path that has failed or is susceptible to failure with the lead path of the present invention. The present invention also recognizes that causes of lead path failure around area A shown in FIG. 2 are relatively unknown. Thus, the present invention also provides assistance in determining causes of lead path failure and identifies ways to overcome lead path failure.
One aspect of the present invention thus involves an apparatus adapted to form a conductive path for carrying an electric current in a generator having a shaft. The apparatus comprises an electrically conductive strap having a first end and a second end, and forming at least a portion of the conductive path. The apparatus also comprises a cleat having at least one axially extending spigot, the cleat adapted to retain the strap between the cleat and a portion of the shaft, the spigot sized and configured to carry at least a portion of a radial load of the strap and at least a portion of an axial load of the strap.
Another aspect of the present invention thus involves a method of retrofitting an electrical lead path in a generator. The method comprises removing a portion of a shaft of the generator to form at least one slot. The method also comprises arranging a conductive portion of the lead path between the shaft and a cleat, the cleat having a general T-shape with a portion that is sized and configured for placement within the at least one slot. The method also comprises attaching the cleat to the rotor so that the cleat can accept at least a portion of a radial load exerted by the strap and at least a portion of an axial load exerted by the strap. Yet another aspect of the present invention thus involves a method of choosing a plurality of electrically conductive components to inhibit electrical failure in a lead path of a generator. The method comprises identifying at least one phenomenon that may cause or tend to cause lead path failure. The method also comprises providing a plurality of components adapted to inhibit the identified at least one phenomenon from causing or tending to cause lead path failure, the plurality of components including a cleat component having at least one tapered spigot and adapted to secure a portion of the lead path and accept stress and load forces from the lead path during normal generator operation. The method also comprises arranging and attaching at least one electrically conductive component to form the lead path.
Further aspects, features and advantages of the present invention will become apparent from the drawings and detailed description of the preferred embodiment that follows.